JPH05104557A - Reactive injection molding method - Google Patents

Abstract

PURPOSE:To prevent the separation of the surface of a molded product from the surface of a cavity during the contraction period of a reaction curing process without altering a material recipe by applying pressure equal to or more than foaming pressure to a molded product during the contraction period of the reaction curing process. CONSTITUTION:A synthetic resin is molded by injecting a mixture of polyether and isocyanate in the cavity 3 of a mold to react both components. At this time, pressure equal to or more than foaming pressure is applied to the molded product through the surface of the cavity 3 during the contraction period of a reaction curing process. By this constitution, the surface of the molded product is not separated from the surface of the cavity 3 even when the molded product is contracted. As a result, the non-uniform pressure distribution on the surface of the molded product is eliminated and the generation of the surface flaw of the molded product can be suppressed without altering a material recipe.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synthetic resin reaction injection molding method.

[0002]

2. Description of the Related Art As one of molding methods of synthetic resin, polyurethane is formed by passing through a mixing head for mixing polyether (A liquid) and isocyanate (B liquid) at high pressure and injecting it into a molding die. Reaction Injection Molding (Reaction I
njection Molding (RIM) (see, for example, JP-A-62-68710).

In the above reaction injection molding, as shown in FIG. 3, the cavity pressure P changes from the start of injection to the completion of mold clamping. The injection conditions at this time are: mold temperature: 70
C, injection amount: 1900 g, injection time: 1.0 sec, air loading in liquid A: 40 vol%, mold clamping time: 15.0 sec, mold clamping pressure: 105 ton.

That is, when injection is started, the cavity pressure P rises to point A (for example, 13 kgf / cm ² ) due to the injection pressure and then drops to point B (for example, 5 kgf / cm ² ). From the time point, foaming by the mixed reaction of both liquids is started, and thereafter, the pressure drops to the point D where the mold clamping is completed through the point C where the foaming pressure becomes the highest.

A typical surface defect of a molded article M obtained by reaction injection molding is a sink mark S (ie, sink mark) shown in FIG. 4, which is made of a material (ie, A liquid and It occurs because the liquid B) is partially separated from the cavity surface and contracts when it is reactively cured in the mold. In FIG. 4, reference numeral 1'is a fixed type, 2'is a movable type,
3'is a cavity.

Possible causes are an imbalance in the curing characteristics of the material formulation, stains or scratches on the cavity surface, and variations in mold release characteristics on the cavity surface.
These occur during the pressure drop period (in other words, the contraction period) from point B to point D shown in FIG. That is, it is presumed that the sink mark is generated due to the uneven pressure distribution in the cavity due to the contraction of the molded product during the pressure drop period.

In order to prevent the occurrence of the above-mentioned surface defects, a method of changing the curing characteristics of the material formulation to reduce the curing rate can be considered, but the physical properties and productivity are often sacrificed. The problem arises.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and the surface of a molded product is not affected by a cavity during shrinkage during the reaction curing process without changing the material prescription. The purpose is to keep away from the surface.

[0009]

In the present invention, as a means for solving the above-mentioned problems, a reaction injection molding method for molding a synthetic resin by mixing and injecting polyether and isocyanate into a mold cavity for reaction. In the above, in the contraction period in the reaction curing process, a pressure higher than the foaming pressure is applied to the molded product through the cavity surface.

[0010]

In the present invention, the following actions are obtained by the above means.

That is, when a pressure higher than the foaming pressure is applied to the molded product through the cavity surface during the contraction period in the reaction curing process, the surface of the molded product separates from the cavity surface even if the molded product contracts. Disappears.

[0012]

According to the present invention, in a reaction injection molding method for molding a synthetic resin by mixing and injecting a polyether and an isocyanate into a mold cavity and reacting them, a molded article is produced during the shrinkage period in the reaction curing process. Since a pressure higher than the foaming pressure is applied through the cavity surface to prevent the molded product surface from separating from the cavity surface even if the molded product contracts, uneven pressure on the molded product surface Since the distribution is eliminated, there is an excellent effect that generation of surface defects (that is, sink marks, pinholes, etc.) of the molded product can be suppressed without changing the material prescription.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the accompanying drawings.

The reaction injection molding of this embodiment is carried out using the mold shown in FIGS.

That is, in the molding die including the fixed die 1 and the movable die 2, the clearance adjusting sealing material 4 made of silicon rubber is arranged on the die mating surface of the fixed die 1 so as to surround the cavity 3. ing. In the case of the present embodiment, the clearance adjustment amount h by the sealing material 4 is set to 200 μm when there is no load. Reference numeral 5 is a mixing head for mixing polyether (A liquid) and isocyanate (B liquid) before injection, 6 is a gate serving as an inlet of the cavity 3, and 7 is a material (A) injected from the mixing head 5.
An auxiliary mixer for mixing the mixed liquid of liquid B and liquid B) even better, 8 is a degassing passage, and 9 is a pressure sensor attached to the cavity surface. In this embodiment, the seal material 4 is provided on the fixed die 1 side, but the seal material 4 may be provided on the movable die 2 side.

The material formulations used in this example were as follows.

Liquid A: polyether polyol (average molecular weight = 3000) 77 parts by weight ethylene glycol 22 parts by weight DABCO (diazabicyclooctane) 33 LV (manufactured by Air Products) 1 part by weight DBTDL (dibutyltin dilaurate) 0.1 parts by weight Part B liquid: Modified MDI (NCO% = 28.7) 98 parts by weight Using the molding die as described above, the mold clamping pressure operation shown in Table 1 below was performed by the material of the above formulation to perform reaction injection molding. .. The injection conditions at this time were: mold temperature: 70 ° C, injection amount: 19
00g, injection time: 1.0sec, air loading in liquid A:
40vol%, mold clamping time: 15.0sec.

[0018]

[Table 1]

In Table 1, O, A, B, C, D
Indicates each point in FIG.

Here, the mold clamping pressure (in other words, the cavity pressure) P is set to 105 tons (15 kgf / cm ² ) between OB (that is, from the start of injection to the start of reaction curing). The reason is that a pressure is required to overcome the injection pressure of the material ejected from the mixing head 5.
Therefore, the clearance h in this period is 120 μm
Has been reduced to.

Next, between B and C (that is, during the foaming pressure rising period), the foaming pressure rises and the volume of the molded article increases as the reaction curing progresses, so that sufficient foaming occurs. The mold clamping pressure (in other words, cavity pressure) P is set to 55 tons (8 kgf / cm ² ) to allow it, and the clearance h is expanded to 170 μm. This provides good reaction cure with sufficient foaming.

During the period between C and D (that is, the foaming pressure drop period), since the foaming pressure drops and the volume of the molded product shrinks, the mold clamping pressure (in other words, cavity pressure) P Foaming pressure (ie, 5 kgf / cm ² shown in FIG. 3)
The larger 140 ton (20 kgf / cm ² ) is raised to reduce the clearance h to 100 μm. As a result, even if the molded product contracts, the surface of the molded product is not separated from the cavity surface, and the uneven pressure distribution on the surface of the molded product is eliminated. Therefore, it is possible to suppress the occurrence of surface defects (that is, sink marks, pinholes, etc.) in the molded product without changing the material prescription.

As in the present embodiment, the fixed mold 1
When a seal member 4 for clearance adjustment is provided between the contact surfaces of the movable mold 2 and the movable mold 2 so that the mold clamping pressure is changed in the reaction hardening process, the plate thickness dimension of the final product is equal to the clearance adjustment amount ( In the case of the above-described embodiment, since h = 100 μm), the cavity depth in the fixed mold 1 should not be a problem if the cavity depth is made shallower by a dimension corresponding to the clearance adjustment.

In the above embodiment, a polyurethane-based reaction injection molding material is used, but it goes without saying that a polyurea-based or polyurethane / polyurea-based material may be used.

[Brief description of drawings]

FIG. 1 is an enlarged sectional view showing a cavity portion of a molding die used in a reaction injection molding method according to an embodiment of the present invention.

FIG. 2 is a plan view of a fixed mold in a mold used in the reaction injection molding method according to the example of the present invention.

FIG. 3 is a characteristic diagram showing changes in cavity pressure during a reaction injection molding process.

FIG. 4 is a partial sectional view of a cavity for showing a state of a molded product obtained by a conventional reaction injection molding method.

[Explanation of symbols]

1 is a fixed type, 2 is a movable type, 3 is a cavity, 4 is a sealing material, and 5 is a mixing head.

Claims (1)

[Claims] 1. A reaction injection molding method in which a synthetic resin is molded by mixing and injecting a polyether and an isocyanate into a mold cavity to react with each other, wherein a molded product is subjected to shrinkage during a reaction curing process. A reaction injection molding method, wherein a pressure equal to or higher than a foaming pressure is applied through a cavity surface.